Background: Throughout the last decades many studies have been tended to investigate, identify and treat different linguistic or non-linguistic errors made by learners in their spoken and written language. Sometimes instructors' errors are involved in few researches also. Aims: This study is concentrated on investigating the linguistic errors (LEs) that were found out in the test sentences (TSs)- interrogatives (InTSs) and imperatives (ImTSs)- made by instructors who are non- native speaker nor specialists in English language. This study aims to answer these questions: 1- Which type of TSs are used more frequently? And why? 2- Are there LEs in these TSs? And what are their categories ? 3- What are the reasons behind committing them? and how can they be avoided? Methods: (323) TSs written in (51) test papers are subjected to the statistical investigation and analysis. These TSs were used to test scientific materials taught in English in Baquba Technical Institute. Conclusions: Results show that ImTSs are used more frequently than the InTSs because the former easily constructed and achieve the same purpose, i.e., elicitation of information. In these TSs, (439) LEs are identified and divided into three categories: syntactic (which is divided into six classes), punctuation and spelling respectively. The reasons behind these LEs are attributed to the shortage in the instructors' competence of the linguistic principles and rules that govern the language construction. Consequently, these instructors use English language but they do not know it systematically. Finally, the present study sets up recommendations to avoid these LEs in the test papers and in other types of writings.